No information on the four was available.
The State Department says it is making arrangements to send them to their home countries, said Rear Admiral James McGarrah, who oversees the reviews of prisoners and whether they should remain at Guantanamo, speaking to reporters at the Pentagon.
Their fate was determined by a quasi-judicial process called an administrative review board, which the Pentagon created after being heavily criticised by human rights groups about the indefinite nature of the detentions at the US naval base.
A three-officer board decides whether each prisoner remains enough of a threat to justify keeping them at Guantanamo; their home governments and family are allowed some input, but they are not afforded legal representation.
Each prisoner can be released, transferred to their home government or kept in detention, indefinitely without trial.
Gordon England, the acting deputy defence secretary, has approved 70 decisions of the board: four releases, 25 transfers and 41 continued detentions, McGarrah said.
About 520 alleged combatants
The board intends to review the cases of most of the rest of the prisoners at Guantanamo at least once a year.
About 520 alleged combatants remain at Guantanamo; another 234 have been released or transferred to the custody of their home governments through various processes and agreements. Of those, 12 have allegedly returned to what the US calls “terrorism”, according to McGarrah.
Several dozen detainees who remain at Guantanamo are slated for release or transfer, McGarrah said.
In some cases, the US government has not received satisfactory assurances they will not be mistreated once they arrive in their home country, leaving them in legal limbo at Guantanamo.
McGarrah claimed these people have more privileges than the rest of the prison population.
The people held at Guantanamo are mostly Afghans, Pakistanis and others captured after the US invasion of Afghanistan in October 2001.
The US labeled them “enemy combatants,” which the Bush administration decided did not to afford them status as prisoners of war under the Geneva Conventions, allowing them to be detained indefinitely without trial.